Weak "false positive" direct antiglobulin test reactions with polyspecific antiglobulin reagents: lack of correlation with red-blood-cell-bound C3d.

The investigation explored whether weak positive or "rough" direct antiglobulin test (DAT) reactions observed with commercial polyspecific reagents could be correlated with the amount of C3d bound to normal donor red blood cells (RBC). Employing a radiolabeled anti-antiglobulin method, RBC-bound C3d was measured on 101 normal donor samples. In a second phase of the study, RBC-bound C3d plus igG were measured on an additional 141 donor samples. In neither phase of the study was a correlation observed between weak positive antiglobulin reactions and the amount of RBC-bound serum globulins.